The known measuring apparatus for checking crankshafts as to location, position and form of the main and connecting-rod bearings can be classified into three categories as delineated below.
The first category consists of so-called multipoint measuring apparatus. In such an apparatus, a separate measuring device is provided for each bearing so that all bearings can be measured simultaneously when the crankshaft is rotated. Such apparatus are very complex and expensive due to the multitude of measuring devices. Also, these apparatus are not very flexible because the measuring devices must be adapted exactly to the geometry of the crankshaft to be checked. For these reasons, such apparatus are normally used only for the 100% inspection of large series. Multipoint measuring apparatus for crankshafts are described, for example, in the corporate publication of Hommelwerke GmbH of Schwenningen, Germany, entitled "Kurbelwellen-Me.beta.maschinen", print no. 8.89 Ko, and in U.S. Pat. No. 4,651,438. A multipoint measuring apparatus suitable for camshafts is described in the international patent publication WO 93/10420.
Coordinate measuring apparatus belong to the second category of measuring apparatus serving the above-mentioned purpose. These apparatus, developed for the measurement of very different workpieces, are quite flexible, but they require long measuring times because all positions must be measured sequentially with the one probe with which the apparatus is equipped.
The third category of measuring apparatus constitute so-called combination measuring apparatus. These are generally configured like a coordinate measuring apparatus having a cylinder coordinate design for rotationally symmetrical workpieces and are equipped with a measuring edge which is used to measure the different bearings sequentially. Here, the connecting-rod bearing slides along the measuring edge. A measuring apparatus having an optical measuring edge is described, for example, in the international patent publication WO 87/07007. Such apparatus are more flexible and less complex than multipoint measuring apparatus, but they do not achieve the short measuring times of multipoint measuring apparatus.
One common feature of the known crankshaft measuring apparatus of all three categories is the fact that the measuring means used to contact the connecting-rod bearings are practically always in direct mechanical contact with the connecting-rod bearings and are entrained by the crankshaft when the same is rotated. For this reason, a considerable measuring force is applied to the connecting-rod bearings to be measured by the measuring devices during the measuring process and this results in corresponding starting vibrations, wear and measuring uncertainties. In order to reduce the measuring forces, the measuring apparatus described in U.S. Pat. No. 4,351,115 and European Patent 0,428,543 employ counterweights to relieve the load on the tracking arm.